Conventionally, in source gas supply devices for semiconductor manufacturing devices, etc., heat-type flow controllers and pressure-type flow controllers have been widely used for controlling the flow of the supply gas. In particular, the latter pressure-type flow controller FCS is, as shown in FIG. 6, composed of a control valve CV, a temperature detector T, a pressure detector P, an orifice OL, a computation control unit CD including a temperature correction/flow computation circuit CDa, a comparison circuit CDb, an input/output circuit CDc, an output circuit CDd, etc., and the like. Such a controller has excellent flow characteristics in that stable flow control can be performed even when the primary-side supply pressure is significantly changed.
That is, in the pressure-type flow controller FCS of FIG. 6, values detected at the pressure detector P and the temperature detector T are input to the temperature correction/flow computation circuit CDa, where the detected pressure is subjected to temperature correction and flow computation, and then the flow computation value Qt is input to the comparison circuit CDb. In addition, an input signal Qs corresponding to the set flow is input from the terminal In and then input to the comparison circuit CDb through the input/output circuit CDc, where the signal is compared with the flow computation value Qt from the temperature correction/flow computation circuit CDa described above. As a result of this comparison, in the case where the set flow input signal Qs is smaller than the flow computation value Qt, a control signal Pd is output to the actuator of the control valve CV. Accordingly, the control valve CV is actuated in the closing direction, and actuated toward the valve-closing direction until the difference between the set flow input signal Qs and the computed flow value Qt (Qs−Qt) reaches zero.
In the pressure-type flow controller FCS, when a so-called critical expansion condition of P1/P2≥about 2 is maintained between the pressure P2 on the downstream side and the pressure P1 on the upstream side of the orifice OL, the gas flow Q through the orifice OL is as follows: Q=KP1 (wherein K is a constant). Meanwhile, when the critical expansion condition is not satisfied, the gas flow Q through the orifice OL is as follows: Q=KP2m(P1−P2)n (wherein K, m, and n are constants).
Therefore, excellent characteristics can be exerted as follows. That is, the flow Q can be controlled with high precision by controlling the pressure P1. Further, even when there is a significant change in the pressure of the gas Go on the upstream side of the control valve CV, the controlled flow value hardly changes.
The pressure-type flow controller designed such that the gas flow Q is computed as Q=KP1 (wherein K is a constant) as described above is generally called FCS-N type. In addition, the pressure-type flow controller designed such that the gas flow Q is computed as Q=KP2m(P1−P2)n (wherein K, m, and n are constants) is generally called FCS-WR type.
Further, as pressure-type flow controllers of this kind, other types called FCS-SN type and FCS-SWR type exist. FCS-SN type uses, as an orifice of the above FCS-N type, an orifice mechanism including a plurality of orifices OL connected in parallel so that gas is allowed to flow through at least one orifice by a switching valve, such as an orifice mechanism including two orifices connected in parallel and a switching valve provided on the inlet side of one orifice so that the flow control range can be changed by opening or closing the switching valve. FCS-SWR type uses the same orifice mechanism as an orifice of the above FCS-WR type.
Incidentally, with respect to the pressure-type flow controllers of FCS-N type, FCS-SN type, FCS-WR type, and FCS-SWR type described above, their own configurations, operation principles, and the like are already known, and thus the detailed description thereof will be omitted herein (JP-A-8-338546, JP-A-2003-195948, etc.).
In addition, as pressure-type flow controllers FCS, as shown in FIG. 7, the following types exist: a pressure-type flow controller FCS configured as shown in (a) for a gas fluid under critical conditions (hereinafter referred to as FCS-N type; JP-A-8-338546, etc.); (b) FCS-WR type for both a gas fluid under critical conditions and a gas fluid under non-critical conditions (JP-A-2003-195948, etc.); (c) flow-switch FCS-S type for a gas fluid under critical conditions (JP-A-2006-330851, etc.); and (d) flow-switch FCS-SWR type for both a gas fluid under critical conditions and a gas fluid under non-critical conditions (Japanese Patent Application No. 2010-512916, etc.).
Incidentally, In FIG. 7, P1 and P2 denote pressure sensors, CV denotes a control valve, OL denotes an orifice, OL1 denotes a small-diameter orifice, OL2 denotes a large-diameter orifice, and ORV denotes an orifice switching valve.
However, in pressure-type flow controllers of this kind, because orifices OL having a fine bore diameter are used, the gas replaceability is low. Thus, in the case where the control valve CV of a pressure-type flow controller FCS is closed to open the output side, it takes a long period of time to exhaust gas in the space part between the control valve CV and the orifice OL, leading to a problem in that the so-called gas step-down responsiveness is extremely low.
FIG. 8 shows an example of the step-down response characteristics of a conventional pressure-type flow controller of FCS-N type at the time of continuous steps. In the present circumstances, under the condition where an air-operated valve (not illustrated) on the downstream side of the orifice OL is opened, and a constant flow of gas is being supplied through the pressure-type flow controller, when the amount of gas supply is stepped down in steps, as compared with the case of a pressure-type flow controller for high flows (polygonal line A), in the case of a pressure-type flow controller for low flows (polygonal line B), it takes a time period of 1.5 seconds or more to complete step-down to a predetermined flow.
More specifically, in the case of FCS-N type and FCS-WR type, when the pressure on the downstream side of the orifice OL1 is 100 Torr, and the flow is to be stepped down from 100% to 1% and from 100% to 4%, each step-down takes a time period of about 1 second or more. However, from the semiconductor manufacturing device (e.g., etcher) side, it is required that the flow be stepped down from 100% to 1% within a time period of 1 second or less.
In addition, in the case of FCS-S type and FCS-SWR type, when the pressure on the downstream side of the orifice OL1 is 100 Torr, and the flow is to be stepped down from 100% to 10% and from 100% to 0.16%, each step-down takes a time period of about 1.2 seconds or more. However, from the semiconductor manufacturing device (e.g., etcher) side, it is required that the flow be stepped down from 100% to 10% within a time period of 1.2 seconds or less.
On the other hand, in order to enhance the step-down response characteristics of the above pressure-type flow controllers, it has been attempted to reduce the internal volume of the gas channel between the control valve CV and the orifice OL as much as possible.
FIG. 9 shows, as an example thereof, a pressure-type flow controller using a main body 2 with the internal volume minimized, configured such that the flow direction of the fluid of the control valve CV is reversed from an ordinary control valve CV, whereby gas flows in through the gap between the outer periphery of the diaphragm valve body 20 and the valve seat 2a, and flows out from the center of the valve seat 2a, thereby allowing for the reduction of the internal volume of the gas flow channel.
However, even in the pressure-type flow controller of FIG. 9, which uses a main body 2 with the internal volume minimized, it is difficult to significantly improve the step-down response characteristics by reducing the internal volume of the gas flow channel. Currently, as shown in FIG. 10, when the rated flow is as low as 10 SCCM, in the case of N2 gas, step-down from 100% to 0% takes a time period of about 1 second, while in the case where the gas is C4F8 (flow factor=0.352260), such step-down takes a time period of about 3 seconds.
Incidentally, in FIGS. 10, C, D, and E show step-down characteristics at a flow of 10 SCCM, a flow of 20 SCCM, and a flow of 160 SCCM, respectively.
In addition, in a conventional pressure-type flow controller, for example, in the case where the control valve CV is closed to interrupt the flow control under the condition where the gas supply line connected to the orifice downstream side is temporarily closed by a switching valve or the like, the internal pressure of the fluid channel may increase due to the minute leakage of the source gas from the control valve CV. As a result, when the flow control is re-started, because of the increased internal pressure of the fluid channel, the responsiveness may decrease due to so-called overshooting in flow control at the time of step-up.
As described above, even in a pressure-type flow controller using a main body with the internal volume minimized, it has been difficult to sufficiently improve the step-down responsiveness characteristics of the pressure-type flow controller, and conventional pressure-type flow controllers still have problems of poor step-down response characteristics in the case where the rated flow is low, etc.